Characterization of tokamak edge plasmas using spectroscopic line profiles

Line shape spectroscopy is a valuable tool both for diagnostic purposes, and for understanding the basic atomic processes in the boundary region of magnetically confined fusion plasmas. We report on the present state of a versatile line shape model including Stark, Zeeman and Doppler broadening for an arbitrary emitter in the divertor or other edge plasmas. Several examples of temperature or density diagnostics based on the use of this model are presented for neutral and ionized carbon, and for hydrogen isotopes. In the case of the Dalpha line, fitting the model to the experimental spectra involves the determination of several parameters and we have thus used an efficient fitting technique based on a genetic algorithm. The results of this analysis, suggesting the existence of a population of neutrals of several hundreds of electronvolts, demand a more detailed study of the line wings. With the help of a simple model, we show that this part of the spectrum might indeed be sensitive to the turbulent fluctuations ubiquitous in edge plasmas.